Method and circuit for rapid field excitation control of electromagnetic devices

ABSTRACT

The method for rapid field excitation control of an electromagnetic device, which includes converting an alternating multiphase voltage into several mutually superimposed unidirectional voltages of respectively different maximal amplitudes to obtain a resultant unidirectional fluctuating excitation voltage, temporarily impressing the fluctuating excitation voltage upon the electromagnetic device during at least one of the magnetic field buildup and decay periods of the device, applying the resultant fluctuating excitation voltage during the buildup period and maintaining the resultant voltage until the current through the device attains a value above that of the continuous energization, terminating the energization by disconnecting the normal operating voltage from the device, impressing upon the device a deenergizing equally poled voltage in response to a first change occurring in the load circuit of the device as a result of the disconnection, said deenergizing voltage being opposed to that of the device and being higher than the operating voltage, and removing the deenergizing voltage in response to a second change occurring in the circuit.

United States Patent Heinz Sehaflersmann [72] lnventors Brake; ErnstTuchen, Jerxen-Orbke; Friede Twellsiek, Milse, Germany [21] Appl. No.17,345 [22] Filed Mar. 6, 1970 [45] Patented Mar. 9, 1971 [73] AssigneeBinder Magnete KG Villingen/Schvvarzw., Germany [32] Priority June 18,1966 [33] Germany [31] P15 14 725.8

Continuation of application Ser. No. 647,171, June 19, 1967, nowabandoned.

[54] METHOD AND CIRCUIT FOR RAPID FIELD EXCITATION CONTROL OFELECTROMAGNETIC DEVICES 13 Claims, 11 Drawing Figs.

[52] U.S. 317/123, 3l7/l48.5,317/l56,321/5 [51] Int. Cl. "01h 47/32 [50]Field ot'Search 317/123,

148.5, 123 (CD), 156; 321/5, (lnquired) [56] References Cited UNITEDSTATES PATENTS 3,330,998 7/1967 Winograd 317/ 148.5X

3,401,310 9/1968 Schaffersmannetal 317/123 Primary Examiner- Lee T. HixAttorneys-Arthur E. Wilfond, Herbert L. Lerner and Daniel J. TickABSTRACT: The method for rapid field excitation control of anelectromagnetic device, which includes converting an alternatingmultiphase voltage into several mutually superimage during the buildupperiod and maintaining the resultant voltage until the current throughthe device attains a value above that of the continuous energization,terminating the energization by disconnecting the normal operatingvoltage from the device, impressing upon the device a deenergizingequally poled voltage in response to a first change occurring in theload circuit of the device as-a result of the disconnection,

said deenergizing voltage being opposed to that of the device and beinghigher than the operating voltage, and removing the deenergizing voltagein response to a second change occurring in the circuit.

PATENTEDMAR 9mm 31569792 sum 2 or 7 Fig.4

CURRENT SUPPLY v I; 100 7 110 fit 85 GEN A L ON-OFF 21-24 4 120 I 90CONTROL AMP METHOD AND CIRCUIT FOR RAPID FIELD EXCITATION CONTROL OFELECTROMAGNETIC DEVICES This application is a continuation ofapplication Ser. No. 647,171, filed 6- 1 9-67, now abandoned.

My invention relates to methods and circuits for rapid deenergizationand/or rapid deenergization of the magnetic system in electrical devicessuch as magnetic clutches, brakes, and valves, lifting magnets, holdingmagnets, as well as any other device comprising a magnetic field windingfor performing a switching function, transmitting, driving or stoppingforces or serving other control functions in various machine tools andprocessing machines or the like.

For a precise operation of such devices it is necessary to attain veryshort time periods for the desired switching operation or otherresponse. Minimizing such time periods, however, is subject tolimitation by delays inherent in the buildingup and decaying of themagnetic field.

For shortening the buildup time of a magnetic field it is known toprovide a rapid excitation circuit wherein an ohmic resistor isconnected in series with the magnetic field winding. This has thedisadvantage of an additional consumption of power which in the seriesresistance is converted into waste heat.

Another rapid excitation system employs an additional voltage which issubstantially higher than the operating voltage and which is switchedoff by time-delayed switching means after the switching-on process hasbeen completed. This requires providing a switching means rated for thegreatly increased voltage and also capable of switching off the fullvalue of increased current subsequent to the switching-on process.Systems of this type are affected by all of the difficulties encounteredwith the interruption of high DC voltages at inductances. If mechanicalcontacts are used, a high degree of contact burning is encounteredunless additional arc arresters are employed. If electronic switches inthe form of semiconductor components are employed, the inductionvoltages must be taken into account and the components must be rated forthe resulting high direct currents. Overcoming these difficulties causesa substantial expense and in some circuits also an undesireable delay ofthe switching off operation.

According to the generally prevailing view in this art, the timenecessary for the deenergization of a magnetic field (also calledsticking time) cannot be reduced below the time that elapses uponinterrupting the energizing circuit by directly opening contacts withoutany spark-arresting means; which means that the shortest attainabledecaying period would be expected if there is no shunt connected inparallel to the magnetic field winding and a portion of the energystored in the field winding is dissipated through the are occurringbetween the switch contacts. This possibility of deenergization, however, has its limitation because the resulting induction voltages areseveral times higher than the normal operating voltage and, whenexceeding a given value, may destroy the magnetic field winding. Theprotective expedients necessary to prevent such destruction result inprolonging the deenergization time.

It is an object of my invention to remove the above drawbacks.

Another object of my invention is to provide a method and electricalcircuit arrangements for the rapid energization and deenergization ofthe magnetic system in electrical devices, wherein the control of theswitching operation is accomplished by electronic circuit components insuch a manner as to secure a reliable and maintenance-free performancewith minimized switching periods as well as minimized energy losses.

Another object of my invention is to accomplish the rapid energizationas well as the rapid deenergization with substantially the same circuitarrangement.

To achieve these objects, and in accordance with the invention, I securea rapid energization ofa magnetic field by deriving from analternating-current multiphase power supply, a unidirectional voltagecomprising a plurality of voltage components superimposed upon eachother and having respective- Iy different maximal values; and I applythe resultant fluctuating direct voltage to the magnetic field windingto be energized until the current through the winding exceeds the normaloperating or rated current of such winding.

According to another feature of the invention, 1 provide for rapiddeenergization by applying a voltage opposing any induction voltage, theauxiliary voltage being switched on in response to changes which occurin the load current circuit of the magnetic device as a result ofinitiating the interruption of that circuit. The opposing voltage has ahigher absolute value than the normal operatingvoltage of the magneticdevice and is switched off in response to the occurrence of anotherchange in said load current circuit.

According to another feature of the invention, it is preferable for therapid deenergization to preset the switching-on point of the opposing ordeenergizing voltage on the trailing edge of its positive half-wave at aconstant value. Thus only the positive deenergizing voltage will havethe necessary magnitude and any additional magnetization dependent uponthe instantaneous value of the energizing voltage is prevented fromoccurring just prior to the beginning of the deenergization period. a

A circuit according to the invention for rapid energizatio and rapiddeenergization of a magnetic field device comprises thyristors forderiving from several phases of a multiphase transformer an increasedvoltage for the rapid energization and deenergization, and monostabletransistor flip-flop stages for controlling the firing of thethyristors. A first arc of the monostable flip-flops determines theduration of the rapid energization. A second one of the flip-flops istimed for the duration of the rapid deenergization, the components ofthe second flip-flop being complementary to those of the first flipflop(PNP and NPN germanium or silicon transistors). The second flip-flop isconnected to a further transistor stage for determining a switching-onpoint of the deenergizing voltage on the positive trailing portion ofits wave. The transistor stage thus provides for synchronization,deriving the required current from the transformer through an RC-member.Preferably the one monostable flip-flop stage has its control input leadand its current supply lead controlled by the switch or other actuatingmember for controlling the energization and deenergization, wherebydisturbances are suppressed.

In order that the invention will be clearly understood, it will now bedescribed, by way of example, with reference to the accompanyingdrawings, wherein FIGS. 1 to 5 (corresponding to FIGS. 1 to 5 in thecopending application Ser. No. 5 15,3 72, filed Dec. 21, 1965, now US.Pat. No. 3,401,310, and assigned to the assignee of the presentinvention) are explanatory, whereas FIGS. 6 to 11 relate to theinvention proper.

FIG. I shows graphs of voltages used according to the invention; i

FIG. 2 is a phase diagram of the voltages across transformer windings inthe circuit arrangement of FIG. 3;

FIG. 3 is the diagram of a circuit for rapidly energizing an electricalapparatus including a magnetic field coil;

FIG. 4 is a more detailed circuit diagram of part of the circuit of FIG.3;

FIG. 5 is a block diagram of a complete system incorporating the detailsof FIGS. 3 and 4;

FIGS. 6 and 7 are the circuit diagrams of different systems embodyingthe present invention and suitable for rapid energization as well asrapid deenergization or magnetic apparatus;

FIGS. 8, 9 and 10 are explanatory graphs of deenergization voltagesemployed according to the invention for assuring that the deenergizingvoltage is switched on at a given cyclical point of time; and

FIG. 11 is a circuit diagram of another system according to theinvention for rapid energization and deenergization of magneticapparatus.

Exemplified in FIG. 1 are time curves of excitation voltages typical ofa system according to the invention, the abscissa denoting time and theordinate values being indicative of voltage amplitudes. The increasedvoltage superimposed upon the field coil of the device to be rapidlyexcited is represented by the curve a. The permanent or steady-stateoperating voltage of the device is shown at b. The particular conditionsdemonstrated by FIG. 1 involve the advantage that the maximum values ofthe rapid excitation voltage a cover the gaps in the steady-state fieldexcitation voltage b. Consequently, when the field winding is beingswitched on at an unfavorable moment, such as at the moment t,, thevoltage impressed upon the winding has at least the maximum value of thenormal operating voltage. The high auxiliary voltage a is showndiscontinued at the moment 1,, assuming that up to this moment themagnetic field has become fully excited so that thereafter only thenormal excitation voltage b is effective.

It should be understood that the voltage diagram of FIG. 1 relates toone phase of an excitation voltage derived from all of the secondaryphases of a three-phase transformer. The vector diagram for all threephases of rectified voltage is shown in FIG. 2. Ia+lb denote therespective vectors of the positive and negative voltages respectively inthe first phase. The vectors Ila and llb are the positive and negativevoltages respectively of the second phase which is connected in serieswith the third phase whose positive and negative voltages are shown asvectors Illa and "lb. The resultant of these voltages is composed offour component vectors each being phase displaced 90 from the adjacentvoltage, the two vectors resulting from Ila, lIIa and Ilb, lllb beingrepresented by broken lines.

Referring now to the system jointly represented by FIGS. 3, 4 and 5, inwhich an excitation performance according to FIGS. 1 and 2 is realized,the magnetic device whose field is to be rapidly excited is exemplifiedby the coil 51 of a contactor. This coil is connected to a three-phasepower supply line 9 (FIG. 4) through a transformer 10 and a group ofcontrolled rectifiers, preferably thyristors. As shown in FIG. 3, thetransformer 10 has six secondary windings denoted by la, lb, Ila, llb,Illa, Illb in accordance with the respective voltage vectors of FIG. 2.The secondary windings Ia, lb, Ila, lIb have a common midpoint connectedto one end of the coil 51 to be rapidly excited. The other end of thecoil 51 is connected to four parallel arranged thyristors 21, 22, 23 and24. The respective other poles of thyristors 23 and 24 are connected tothe free ends of windings Ia and lb respectively. The correspondingpoles of thyristors 21 and 22 are connected in series with therespective windings lIIb and "la to the free ends of respective windingsIIb and Ila. The thyristors 21 and 22 serve to supply the contactor coil51 with steady-state excitation in accordance with the voltage b inFIG. 1. The thyristors 23 and 24 conduct only during the building-upinterval of the magnetic field of coil 51 and hence are connected in acircuit of increased voltage, this being indicated by greater length oftransformer windings Ia, lb. The thyristors 23, 24 are to be turned offupon completion of the rapid excitation stage, whereafter only thethyristors 21 and 22 are to remain in operation.

This particular control of the thyristors is effected by the circuitmeans separately illustrated in FIG. 4 and described presently. Theexcitation current I flowing through the magnet coil 51 causes a voltagedrop in an IR-drop resistor 62 connected in series with the coil 51.This voltage is applied through a resistor 63 to a capacitor 64, bothconstituting an RC-member. A transformer 80 has its primary winding 81connected through a diode 84 across the same capacitor 64. Thepotentiometer 85 permits adjusting the current intensity for rapidexcitation in the circuits, 81-84-64-63-62. This current intensity is ameasure of the counter voltage to be formed at the capacitor 64 andconsequently also determines the moment when the rapid excitation isdiscontinued. In other words, by adjusting the potentiometer 85, theduration of the rapid excitation stage can be preadjusted or varied asmay be desired.

The initially uncharged capacitor 64 represents a short circuit for thetransformer primary winding 81 relative to the high frequency of thefiring voltage supplied by the output circuit 120 (FIG. 4) of anamplifier 120 (FIG. 5) as more fully explained below. Thesecondary'winding 82 of the auxiliary transformer is series connected inthe primary circuit of a transformer 71 which supplies firing pulses tothe thyristors 23 and 24. The secondary winding 82, therefore, has thelow inductive impedance required by the firing circuit in which thetransformer 71 is connected. As soon as the capacitor 64 is fullycharged, its voltage is higher than the voltage at the transformerprimary winding 81. Now a current attempts to flow through the diode 84in the opposite direction, thus blocking this diode. Since now thecurrent can no longer flow in the primary winding 81, the inductiveimpedance of the secondary winding 82 increases considerably and therebyprevents a sufficient firing current from passing through thetransformer 71. As a result, the firing of the thyristors 23 and 24ceases. With the next zero passage, that is, when the cycle period ofthe voltage is terminated, the rapid excitation stage is concluded sincethe increased voltage is no longer present.

The circuit of the secondary winding 82 shown in FIG. 4 has a diode 76connected across the series connection of winding 82 and the primarywinding of the firing-circuit transformer 71. The diode 76 serves toalways secure the same polarity of the voltage in the circuit 120 tomake certain that the thyristors 21, 22, 23 and 24 can be fired.

The primary winding of another firing transformer 72 for the thyristors21 and 22 is connected to the firing circuit 120 in series with aresistor 75 which compensates the ohmic share of the winding 82.

It will be recognized that the switching from rapid excitation to normalexcitation is effected without mechanical contacts and in dependenceupon the operating current of the magnetic field winding being excited.If voltage fluctuations occur in the alternating-current supply line,they automatically result in shortening or prolonging the rapidexcitation stage. Analogously, an increased induction of the magnet coilis overcome by an automatic prolongation of the rapid excitation stage.

The overall diagram of the system shown in FIG. 5 represents the controlnetwork of FIG. 4 by the block marked 60. The diagram of FIG. 5analogously illustrates by blocks all of the above-described othercomponents and also indicates further features relating to theproduction of the firing voltage.

The firing voltage is derived from the multiphase power supply line 9through the above-mentioned transformer 10. Produced from the output oftransformer 10 is a direct voltage exhibiting only a slight ripple andhence having a low contents of harmonics. A conventional astableflip-flop, such as an astable multivibrator 110, is connected to thedirect voltage and furnishes a square-wave output voltage at a frequencywhich is a multiple of the 50 or 60 c.p.s. line frequency. Thesquarewave frequency, for example about 2 k.c.p.s. is applied through anactuator or control unit to the above-mentioned amplifier 120 and thenceto the firing-circuit transformers 71 and 72 as described with referenceto FIG. 4. The unit 90 contains any desired on-off control means forstarting and stopping the current supply to the field winding 51.

lnterposing an amplifier 120 between the frequency generator and thetransformers 71, 72 permits operating the control unit 90 at lower powerso that it may be equipped with transistors or to be controlled by light(photoelectric) barriers, punch tapes, sound tracks or the likeinformation carriers. However, if the output of unit 90 is sufficientfor directly energizing the transformers 71, 72, the amplifier can bedispensed with. Since the greater part of the apparatus forms part ofthe network connected to the power supply line, this applying forexample to the transformers, rectifiers and astable flip-flop, the majorportion of the apparatus may be used for any desired number of magneticdevices simultaneously the remaining portion required for any particulardevice 51 being very small so that the device affords a highlyeconomical use.

The control system may also be modified in various respects, for exampleby providing a smaller or larger number of phases or providing adifferent number of controllable rectifiers or thyristors. Thediscontinuance of the increased voltage (rapid excitation) may bereadily effected in some other way, for example by providing a switch onthe magnet being excited, in dependence upon a rotary movement of amagnetic coupling being excited by the control system, and in someanalogous position-responsive or condition-responsive manner. While weprefer providing the system with semiconductor rectifiers, the systemmay instead be equipped with tubes or transductors (controlled saturablereactors or magnetic amplifiers).

In a system of the type described, the deenergization of the magneticfield winding, that is the time required for the field to decay from itsfull value down to substantially zero, can be further shortened to aconsiderable extent by applying the method and means according to thepresent invention, now to be explained with reference to FIGS. 6 to 11.

The continuous operating DC voltage produced by rectifying the linevoltage, causes a current flow in a given direction, which determinesthe direction of the induction current which continues to flow after thethyristors are turned off. According to the invention such inductioncurrent is counterbalanced without interruption by an opposing currentcaused by the auxiliary opposing voltage which is higher than thecontinuous operating voltage and of the opposite polarity. For thispurpose, advantage is taken of the normally undesirable characteristicof semiconductors to block the flow of current, independently of thepolarity of the applied voltage, only then when the current begins toflow in the reverse direction. This means that the instantaneous valueof the applied voltage must be higher than the induction voltage.

Accordingly, the energy storedin the magnetic field winding is opposedby a several times higher energy which, in accordance with its potentialdifference, will instantaneously tend to drive a current through themagnetic field winding in a direction opposed to that of the inductioncurrent. Any remanent field will be compensated by the further increaseof the negative (counter) current. By properly dimensioning the circuitcomponents, the deenergization is completed within one-quarter cycle,which corresponds to 5 msec. if the line frequency is 50 c.p.s. Stillshorter deenergization periods are attainable with higher frequencies.

According to the method of the invention, the application of theauxiliary opposing voltage is controlled in response to changesoccurring in the load circuit of the field winding due to the initiationof the circuit interruption. Among these changes are:

l The decrease of the operating current;

2. the prolongation of the conducting state of the thyristor lastoperated in forward conduction; and

3. the change of one or several of the thyristors from onto off-statedueto cessation of the firing pulse.

Any other interruption-dependent change in the load circuit may-also beused for controlling the application of the opposing voltage, providedit is followed by a further change at the end of the deenergizingoperation, for example:

I. by decrease of the operating current to zero, or

2. by termination of the prolonged conduction of the thyristor lastoperated,

3. or by the event that, after one or several of the thyristors havechanged to the off-state, the remaining thyristors ultimately alsochange to the off-state.

The method just described is performed by the system illustrated in FIG.6. This system is adapted for rapid energization as well as for rapiddeenergization. As far as rapid energization is concerned, the circuitof FIG. 6 corresponds substantially to that of FIG. 4, the samecomponents being designated by the same reference numerals. Contrary toFIG. 4, however, the system of FIG. 6 comprises a diode 65 connectedbetween the capacitor 64 and the resistor 63. The rapid energizationoccurs as described with reference to FIG. 4.

For rapid deenergization, the system of FIG. 6 is further provided withan additional transformer 73 whose primary winding is connected througha diode 85 to the capacitor 64. The secondary windings of transformer 73are connected through diodes 86 and 87 to the thyristors 23 and 24. Thesecondary windings of the transformer 71 are connected to the samethyristors 23 and 24 through respective diodes 88 and 89.

The rapid deenergization, according to the invention, takes place asfollows:

The deenergization of the magnetic field winding 51 is initiated byinterrupting the control voltage in circuit 120. This stops the firingof thyristors 21 and 22. The current flowing through winding 51decreases and, accordingly the voltage drop of resistor 62 becomessmaller. The capacitor 64 discharges through the diode 85 and thetransformer 73. The change in current through the primary winding oftransformer 73 induces a voltage in the secondary winding of transformer73. Such voltage fires either thyristor 23 or thyristor 24, dependingupon which of the thyristors in that instant has applied thereto apositive potential. A current will continue to flow through the firedthyristor even after the voltage has passed through its zero value. Suchcurrent, however, will be maintained only as long as the instantaneousvalue of the induction voltage is higher than the instantaneous value ofthe increased energizing voltage. Since the increased voltage is severaltimes as high as the operating voltage, such current will become zerobefore the negative peak value is reached. As soon as the currentchanges its direction, the fired thyristor, either 23 or 24, will changeto its off-state. Since the firing voltage has decayed prior to suchchange in current direction, no new firing ofa thyristor will takeplace.

As a result, the induction voltage decays and the induction currentdecreases to zero within a'quarter of a cycle. The small negativecurrent has a beneficial influence on the remanent field of the magneticwinding. In this manner the invention achieves a most rapiddeenergization, which prevents the occurrence of excessively increasedinduction voltages.

The deenergization periods thus attainable are substantially shorterthan those resulting from a direct opening of the circuit by means ofmechanical contacts.

A further advantage of the electronic systems according to the inventionresides in the fact that the time previously neces sary for theelectromechanical actuation of contacts, is at viated. Since further, noarcing periods need be taken into account, the total reduction of timedelays is substantial. Another advantage of the above-describedembodiment of the invention (FIG. 6) is the fact that the improved rapiddeenergization is achieved by simply adding a small transformer :70 andsix diodes to the previously proposed system (FIG. 4).

The same result is accomplished, according to the invention, byeffecting the control of the rapid deenergization in response to thecurrent which, subsequent to the interruption of the control voltage,continues to flow through the thyristors 21 and 22. The requiredsynchronization is secured by having the last operating thyristorcoordinated to a predetermined other thyristor. Such a circuit may, forexample, include an RC-member tuned'in such a manner that the firingvoltage is not reached within the duration of a half-cycle but becomeseffective after elapse of such duration.

A system embodying the type of performance just described is exemplifiedin FIG. 7. In this system the thyristors 21 and 22, normally used tosupply the operating current, are also employed as switches forcontrolling the rapid energization as well as the rapid deenergization.This is especially advantageous because the firing of the thyristors isalways effected by pulses having steep leading and trailing flanksaiidbecause for deenergization only that one thyristor is fired which, inthe phase sequence, most closely follows the negative voltage. Due tothe fact that the induction current now flows through one of thethyristors 23 or 24, the thyristor last traversed by the normaloperating current will go to the offstate and the firing voltage will beswitched off before the deenergization is terminated. I

The control operation of the system according to FIG. 7 is as follows:

The firing voltage is supplied continuously to the terminals 120" andhas preferably steep leading and trailing flanks and a frequency ofabout 2 kc. The thyristors 21 and 22 in the load circuit of the magnetwinding 51 receive firing voltage through a small transformer 70 when acontrol switch 90 is closed. Closing of switch 90 also completes therapid-excitation circuit, since the thyristors 23 and 24 are immediatelyfired through the following circuits: terminals 120" transformer 72thyristor 21 transformer 71 transformer 80 thyristor 23; and transformer72 thyristor 22 transformer 73 transformer 80 thyristor 24. Diodes 83and 89 serve to block current flow in undesired directions.

Subsequent to the switching on, the rapid excitation operation isterminated as follows. The voltage at the terminals of the magneticfield winding 51, which is dependent upon the operating voltage, chargesthe capacitor 64 through the resistor 63. During charging a current alsoflows through the winding 81 of the transformer 80. When the capacitor64 is charged its voltage exceeds the voltage of the winding 81 and, asa result, no more current can flow through the secondary winding oftransformer 80. Hence the reactance of the primary windings 82a and 82bincreases substantially so that the firing current flowing fromtransformer s 71 and 73 is no longer sufficient to fire the thyristors23 and 24. This terminates the rapid excitation operation. I

The deenergization according to the invention works as follows. Afteropening the primary circuit of transformer 70 at the switching member90, the firing voltage of thyristors 21 and 22 is switched off. However,since semiconductor thyristors (four-layer diodes) continue to conductuntil the current passes through zero, the firing circuit remains closedfor one thyristor 23 or 24 in the circuit supplying the increasedvoltage. Due to thyristors 21 and 22 being switched off, the voltage ofthe load circuit decreases whereby the capacitor 64 is discharged. As aresult the blocking action of transformer 80 is removed and eitherthyristor 23 or 24 is fired. When now the voltage passes through zero,the last conducting thyristor 21 and 22 changes to its off-state and theremaining firing voltage from transformer 72 is thus switched off. Atthis time a thyristor in the circuit supplying the increased voltagecontinues to conduct the induction current after the positive voltagehas become zero. Thus again, the induction voltage is opposed by thesubstantially higher increased negative voltage, and as soon as thenegative voltage exceeds the induction voltage the current passesthrough zero and then flows in the opposite direction, thus turning thelast conducting thyristor off. This completes the switching offoperation. For all practical purposes the switching off is accomplishedwhen the current and thus the induction voltage becomes zero because aslight negative current is sufficient to change the thyristor to itsnonconducting state. The deenergization of the field winding 51 isassured within the one-half cycle period during which theabove-described operations take place.

The method according to the invention will be further explained withreference to FIGS. 8to 10, showing how the switching-on instant of thedeenergizing voltage, having a higher absolute value than the operatingvoltage, is predetermined to occur on the trailing portion of thepositive halfwave at a constant amplitude value. In each of FIGS. 8, 9and the abscissa denotes time and the ordinate denotes voltage.

FIG. 8 shows the waveform of the increased deenergizing voltage a whichis also employed as the rapid excitation voltage. The continuousoperating voltage is represented by curve b. The switching-on instant isshown at point 6. Point 11' designates the end of the deenergizingoperation. The deenergizing voltage becomes zero at point e. Denoted byt and t are the beginning and end of a time duration. The heavy-linecurve shown results from the following sequence of operational steps.

When the operating voltage b is switched off at any arbitrary point oftime between t, and t the firing of the thyristors will cease, and thedeenergizing voltage will always occur at point c which occurs not laterthan at the moment The point c was intentionally placed somewhat abovethe maximum amplitude of the curve b, so that the switched-on voltageaccording to curve a will block the thyristors in the circuit whichnormally is energized by the voltage according to curve b.

A synchronizing circuit assures that the deenergizing voltage b isswitched on at point c. The synchronizing circuit is made effective inresponse to the control member in FIG. 7) that initiates thedeenergization of the magnetic field. Such synchronizing circuit, may,in a manner known as such, comprise a zener diode and an RC-member or itmay comprise a pulse-forming circuit, for instance, a Schmitt-triggercircuit.

It is an advantage of the above-described rapid deenergization systemthat only that portion of the positive increased voltage is switched onthat is indispensable for deenergization. The fixing of the switching-oninstant at point c prevents the deenergizing voltage from starting withthe peak value of curve a, for example when the firing voltage happensto be switched off at the moment t,. If this occurred, thedeenergization would require correspondingly more time, and point dwould be located closer to the negative peak of curve f as is shown inFIG. 9 where f designates the negative half of curve a. It follows thatstarting the application of the deenergizing voltage at point c does notintroduce any additional delay into the deenergization. On the contrary,the avoidance of a higher positive voltage has the effect of shorteningthe deenergizing period, a fact apparent from a comparison of FIG. 8with FIG. 9.

FIG. 10 shows the voltage curves for the case wherein the switching-offprocess is started during the period between t and The sequence ofoperational steps then is as follows:

Since the synchronization moment 0, cannot be reached, the positiveoperating voltage b goes through zero at moment t and follows itsnegative half-wave whereby a deenergization already begins. At a momentcorresponding to point of the preceding half-wave, the thyristors 23, 24in the circuit supplying the increased voltage start conducting (pointThe deenergization is completed at a point of time designated by d (eWhere an increased deenergizing voltage is employed with but one phase,the time spacing between points 0, and c will correspond to one-half ofa cycle period. This duration may occur as the maximum switching delay.If desired, the deenergization time can be further reduced by employingphaseshifted voltages.

It will be recognized that a substantial shortening of thedeenergization is achieved by giving the deenergizing voltage apredetermined waveform. Undesirable heating of the magnetic fieldwinding by high current peaks or shocks is avoided, this being ofadvantage particularly where high switching frequencies are involved.

Another advantage of the invention is the fact that the fullenergization may be restarted at any instant of a progressingdeenergization by simply restoring the firing voltage and thuspreventing the deenergization from being completed. Furthermore, therapid deenergization may be started at any instant while a rapidenergization is in progress.

FIG. 11 illustrates a preferred system which affords rapid energizationas well as rapid deenergization with a minimum of circuit components.

A multiphase transformer 210 has its primary windings 211 connected to amultiphase power supply line RST and serves as the voltagesource for acontrol device and as a current supply for a magnetic apparatus 270. Aset of secondary windings 212 furnishes the control voltage which in arectifier 220 is rectified by diodes 221, 222, 223 and smoothed by acapacitor 224. A two-phase secondary winding 213 is used to produce arapid energizing voltage which is preferably rated to correspond to amultiple of the normal operating voltage. For example, the voltage ofwinding 213 may correspond to four times the normal operating voltagesupplied by further secon' dary windings 214.

A set 230 of controlled rectifiers is preferably equipped withthyristors. Two thyristors 231 and 232 supply the increased rapidenergizing voltage to the magnetic apparatus 270. Two other thyristors233 and 234 conduct the normal operating current. The control voltagefurnished by rectifier 220 is connected to a control circuit whichcomprises transistor flip-flop stages 240, 250 and a synchronizing state260 for producing a firing pulse for the thyristor group 230. The systemis controlled by a switch 290 and operates as follows:

Upon closing of the switch 290, the first transistor flip-flop stage240, depending on its setting (set or reset), supplies a firing pulse tothe thyristors 230. Upon opening of switch 290, the second transistorflip-flop state 250 in conjunction with the synchronizing stage 260furnishes a short firing pulse to the same thyristor group 230. Thefiring voltage required for the thyristors 230 to be turned on, issupplied directly through the switch 290. The synchronizing stage 260 isconnected to a phase-shifting stage 280 by whose phase shift the desiredsynchronizing point is secured. This group of circuits 260, 280 isarranged in such a manner that a differing connection of the transformer210 does not affect the phase relation. The magnetic apparatus 270 maybe supplied with a voltage for rapid energization as well as for rapiddeenergization.

A capacitor 414 is normally charged through series resistors 412 and415. Upon closure of the switch 290 the polarity of the capacitor chargeis changed through a diode 417.

The emitter of a transistor 24] of flip-flop 240 is connected to a point418 which is initially at zero potential. Upon closure of the switch 290however, the point 418 receives a positive voltage. As a result, thetransistor 241 is turned off and a transistor 242 of flip-flop 240 isturned on. Transistor 242 connects the thyristors 231 and 232 to thefiring voltage furnished by the control circuit common to allthyristors. Thus, the circuit for rapid energization of the magneticapparatus 270 is closed. The supply of voltage is sustained by thetransformer windings 213.

The above-described switching on of the rapid energization in practicerequires about 10 microseconds. For comparison, the conventionalswitching by means of electromagnetically actuated contacts requiresabout 10 msec.

When the capacitor 414 has discharged through an adjustable resistor 413and the resistor 415, the transistor 241 changes from off to on. Thisalso causes the transistor 242 to be turned on, and the firing voltagefor the thyristors 231 and 232 is switched off. Thus the duration ofrapid energization is determined by the discharge time of the capacitor414. The thyristors 233 and 234 which upon closing of the switch 290 areconnected to the control voltage, carry the normal operating currentafter termination of the rapid energization.

Thus, the switching-on operation characterized by the rapid venergization of the magnetic apparatus 270, is completed. The

operational switching on of the magnetic apparatus 270 takes placethrough the already fired thyristors 233 and 234 whose firing currentcontinues to flow through the closed switch 290.

For inactivating the magnetic apparatus 270, the switch 290 is to beopened. This operates the second transistor flip-flop stage 250 asfollows.

The semiconductor junction components of the second stage 250 arecomplementary to those of the first stage 240. For example, the secondstage may comprise NPN silicon transistors 251 and 252 whereas the firststage comprises PNP germanium transistors 241, 242.

A voltage divider of the second stage comprising resistors 515 and 516defines initially the charge polarity of a capacitor 514. Upon openingof the switch 290 a negative abrupt change of potential takes placeacross the capacitor 514 so that now the capacitor discharges throughthe adjustable resistor 513 and the resistor 516. During such discharge,which is limited to the duration of one-half of a cycle, the silicontransistor 251 is nonconducting so that the base of the silicontransistor 252 is connected to positive potential whereby transistor 252is turned on.

A positive voltage is applied through resistors 511 and 611 to thecollector ofa transistor 261 in the synchronizing stage 260, whereby thetransistor 261 is in a state of readiness for 10 msec. subsequent to theopening moment of the switch 290. The base of the transistor 261 in thesynchronizing stage 260 is connected to a circuit 280 for producing apulsating direct voltage which, on the average, is shifted in phase by45 rela tive to the normal operating voltage. For producing thepulsating and phase-shifted direct voltage from an alternating voltage,the circuit 280 comprises a series connection of an inductance, formedby a winding 215 of the transformer 210, a resistor 28] and a rectifier283. This direct voltage is applied to the base of the transistor 261which thus periodically switches on and off at intervals of 10 msec.

The timing of synchronizing stage 260 is such, that the transistor 261is on for 9 msec. and off for l msec. That is, the transistor is turnedoff for 0.5 msec. at the beginning and at the end of each cycle.

When the silicon transistor 261 is turned off, a positive voltage isapplied to the firing electrodes of the thyristors 231 and 232. Hencethe thyristors will be switched on each time at a predetermined point onthe trailing portion of the half-wave of the rapid deenergizationvoltage. Since this switching takes just 1 msec., only the one thyristorwill be fired that will conduct the operating currentin the forwarddirection. The firing point appears approximately at of each half-wave.The increased rapid energizing voltage at such point is higher than thenormal energizing voltage. Therefore, either thyristor 231 or 232 beginsto conduct and the current, upon passing through zero, continues flowingduring its negative half-wave. Since now the firing voltage has ceased,the induction voltage of the magnetic apparatus 270 is opposed by thenegative increased voltage and the switching off takes place at theinstant when the current passes through zero. The performanceexemplified can also be carried out if the transistors of the twoflip-flop stages which differ from each other (NPN; PNP) are used inanother suitable combination.

The above-described system requires a minimum of circuit components andis applicable wherever a rapid current rise is desired inelectromagnetic devices, including electric motors and generators. Thesystem may be modified for special cohtrol purposes, for example byomitting the thyristors 233, 234 for carrying the operating current ifmerely a pulse excitation rather than continuous excitation is desired.There are also uses that permit omitting the first transistor flip-flopstage, for example where a rapid deenergization but no rapidenergization is desired. 1

In a control system accordingto the invention, the voltage for rapidenergization and for rapid deenergization is derived from a multiphasetransformer. This has the advantage that the impulse load resulting fromthe rapid energization is distributed over several phases. Furthermore,a transformer of a given size affords drawing a pulse or shock powerhigher than rated continuous power, and the pulse load derived from thetransformer has no disturbing effect upon the control voltage derivedfrom the same transformer. Taking the rapid energization voltage and thenormal operating voltage from a singlephase transformer, would requireproviding considerably more smoothing means for the control voltage anda much higher sensitivity to disturbances would be encountered.

Due to the fact that monostable complementary flip-flops are employedfor producing the firing voltage for the thyristors, the number ofcircuit components is substantially reduced since the need for theinterposition of inverter stages is obviated. A fact that alsocontributes to minimizing the time delays involved in the performance ofthe system and permits reducing the necessary biasing current for thetransistor circuits.

Deriving of the current for the synchronization from the transformerthrough an RC-member assures by the resulting phase shift a faultlessoperation irrespective of the particular phase connections of themultiphase transformer to the power line. A rotating primary fielddiffering in phase or phase rotation from another rotating field doesnot have any influence, so that a wrong phase connection of thetransformer to the power supply line is impossible.

The leads of the control electrodes and of the currentsupply electrodeof the first or input transistor flip-flop stage extend through thecontrol member 290 in order to suppress disturbing influences. Due tosuch connection a spurious voltages or potential shifts on the supplyleads of the control member 290 do not affect the control performance.By virtue of these features, the invention lends itself readily to beingrealized in existing systems by merely adding the needed additionalcomponent and without substantially changing the wiring of the existingsystem. In addition, the wiring required for the purposes of theinvention does not necessarily require screening or shielding.

The variable resistor 413 has been provided in the flip-flop stage foradjusting the duration of the increased rapid energization voltage. Thisaffords an economical production due to the resulting adaptability ofthe system to different magnetic devices.

It is to be understood that the invention is not limited to theparticular embodiments described and shown, but that it comprises anymodifications and equivalents within the scope of the appended claims.

We claim:

1. Method of rapid deenergization of an electromagnetic device, whichcomprises disconnecting the normal operating voltage from the device,impressing upon the device a deenergizing equally poled voltage inresponse to a first change occurring in the load circuit of the deviceas a result of the disconnection, said deenergizing voltage beingopposed to that of said device and being higher than the operatingvoltage, and removing said deenergizing voltage in response to a secondchange occurring in said circuit.

2. The method of claim 1, for rapid energization as well as rapiddeenergization of an electromagnetic device, which comprises convertingand alternating multiphase voltage into several mutually superimposedunidirectional voltages of respectively different maximal amplitudes toobtain a resultant unidirectional fluctuating excitation voltage,temporarily impressing said fluctuating excitation voltage during amagnetic field buildup period of the device and maintaining saidresultant voltage until the current through said device attains a valueabove that of the continuous energization, the energization beingterminated by the disconnection of the normal operating voltage from thedevice.

3. The method of claim 1, which comprises setting for said equally poledvoltage a switching-on point having a predetermined constant amplitudevalue on the trailing portion of the positive half-wave of said equallypoled voltage.

4. The method of claim 1, wherein said first change is the occurrence ofa given difference between the mean value of the normal operatingcurrent and the induction current of said load circuit, and wherein saidsecond change is the zero passage of the current in said load circuit.

5. A system for rapid field excitation control of an electromagneticdevice, comprising direct-current supply means having a load circuitincluding said device for providing normal operating voltage thereforand having control switch means for switching said operating voltage onand off; multiphase alternating-voltage supply means having a pluralityof mutually phase-displaced output voltages of respectively differentamplitudes, controllable rectifiers connecting said respective outputvoltages to said load circuit for applying rectified auxiliary voltagesupon said load circuit when said rectifiers are conductive,condition-responsive control means connected to said rectifiers forcontrolling them to conduct only during a given interval of time,circuit means for effecting removal of said auxiliary voltages, saidcontrol means being in connection with said load circuit and responsiveto respective first and second changes occurring in said load circuitdue to opening of said control switch means so as to apply saidauxiliary voltages during decay of the field of said device, saidauxiliary voltages forming a resultant fluctuating voltage opposed tothe induction voltage of said device for shortening said decay 6. Asystem according to claim 5, comprising a multiphase power supplytransformer, said direct-current supply means comprising controlledrectifier means connected to said transformer for providing said normaloperating voltage, said trans former forming part of saidalternating-voltage supply means, and said resultant fluctuating voltagehaving a higher absolute value than said operating voltage.

7. In a system according to claim 6, said condition-responsive controlmeans being responsive to the forward current which in said load circuitcontinues to flow through said controlled rectifier means upon openingof said control switch means, whereby said forward current constitutessaid first change which causes said resultant auxiliary voltage to beapplied.

8. A system for rapid field excitation control of an electromagneticdevice, comprising direct-current supply means having a load circuitincluding said device for providing normal operating voltage thereforand having control switch means for switching said operating voltage onand off; multiphase alternating-voltage supply means having a pluralityof mutually phase-displaced output voltages of respectively differentamplitudes, controllable rectifiers connecting said respective outputvoltages to said load circuit for applying rectified auxiliary voltagesupon said load circuit when said rectifiers are conductive,condition-responsive control means connected to said rectifiers forcontrolling them to conduct only during a given interval of time, saidcontrol means being in connection with said load circuit and responsiveto respective first and second changes occurring in said load circuitdue to opening of said control switch means so as to apply saidauxiliary voltages during decay of the field of said device, saidauxiliary voltages forming a resultant fluctuating voltage opposed tothe induction voltage of said device for shortening said decay, amultiphase power supply transformer, said direct-current supply meanscomprising controlled rectifier means connected to said transformer forproviding said normal operating voltage, said transformer forming partof said alternating-voltage supply means, and said resultant fluctuatingvoltage having a higher absolute value than said operating voltage, saidconditionresponsive control means being responsive to the forwardcurrent which in said load circuit continues to flow through saidcontrolled rectifier means upon opening of said control switch means,whereby said forward current constitutes said first change which causessaid resultant auxiliary voltage to be applied, said conditionresponsivecontrol means being responsive to at least one of said rectifier meansin said load circuit changing to the offstate, whereby said change ofstate constitutes said first change which causes said resultantauxiliary voltage to be applied; and said condition-responsive controlmeans being further responsive to another one of said rectifier meanschanging to the off-state, whereby said latter change causes saidresultant auxiliary voltage to be switched off.

9. A system according to claim 5, comprising a synchronizing stageconnected with said control switch means and with saidcondition-responsive control means for securing a given switching-onpoint of said fluctuating auxiliary voltage relative to its cycleperiod.

10. A system according to claim 5, comprising a multiphase transformerhaving a plurality of secondary windings, first and second controllablerectifier means having respective control electrodes, said firstcontrollable rectifier means being connected to respective ones of saidsecondary windings and to said device for supplying an operating fieldvoltage to said device, said second controllable rectifier means beingconnected to other ones of said secondary windings and to said devicefor supplying an increased auxiliary field voltage to said device,firing control circuit means comprising three firing circuits, a firstone of said firing circuits being connected to said control electrodesof said first rectifier means, a second and the third one of said firingcircuits being coupled to said first firing control circuit andconnected to said control electrodes of said second rectifier means,sensing circuit means coupled to said second and third firing circuitsand thereby to said first firing circuit for discontinuing the firing ofany one of said first and second rectifier means in response to sensingof a change in the excitation of said device; control switch meansarranged in said first firing circuit for closing said first firingcircuit to cause initial energization of all of said rectifier means,said sensing circuit means being adapted, when responding, to causeblocking of said second rectifier means after a predetermined periodfollowing the closing of said switch means. said switch means being alsooperative to cause blocking of said first rectifier means when saidswitch means is opened.

11. A system according to claim 10, comprising a further rectifiercircuit for energizing said firing control circuit means, said firingcontrol circuit means comprising flip-flop means connected between saidfurther rectifier circuit and the control electrodes of said secondrectifier means, and synchronizing means in said firing control circuitmeans for setting the firing of said second rectifier means at apredetermined point relative to the wave of the increased voltage.

12. in a system according to claim all, said flip-flop means comprisingtwo monostable flip-flop stages of which each has componentscomplementary to those of the other flip-flop stage, said flip-flopstages having control electrodes and supply electrodes and outputelectrodes, the control and supply electrodes of at least one of saidflip-flop stages being couple through said control switch means to saidfurther rectifier circuit, said synchronizing vmeans comprising an RCmember for connecting the synchronizing means to one of said secondarywindings of said transformer.

13. In the system according to claim 12, said one monostable flip-flopstage comprising an adjustable member connected to said controlelectrode for adapting the circuit arrangement to respectively differentelectromagnetic devices.

1. Method of rapid deenergization of an electromagnetic device, whichcomprises disconnecting the normal operating voltage from the device,impressing upon the device a deenergizing equally poled voltage inresponse to a first change occurring in the load circuit of the deviceas a result of the disconnection, said deenergizing voltage beingopposed to that of said device and being higher than the operatingvoltage, and removing said deenergizing voltage in response to a secondchange occurring in said circuit.
 2. The method of claim 1, for rapidenergization as well as rapid deenergization of an electromagneticdevice, which comprises converting and alternating multiphase voltageinto several mutually superimposed unidirectional voltages ofrespectively different maximal amplitudes to obtain a resultantunidirectional fluctuating excitation voltage, temporarily impressingsaid fluctuating excitation voltage during a magnetic field buildupperiod of the device and maintaining said resultant voltage until thecurrent through said device attains a value above that of the continuousenergization, the energization being terminated by the disconnection ofthe normal operating voltage from the device.
 3. The method of claim 1,which comprises setting for said equally poled voltage a switching-onpoint having a predetermined constant amplitude value on the trailingportion of the positive half-wave of said equally poled voltage.
 4. Themethod of claim 1, wherein said first change is the occurrence of agiven difference between the mean value of the normal operating currentand the induction current of said load circuit, and wheRein said secondchange is the zero passage of the current in said load circuit.
 5. Asystem for rapid field excitation control of an electromagnetic device,comprising direct-current supply means having a load circuit includingsaid device for providing normal operating voltage therefor and havingcontrol switch means for switching said operating voltage on and off;multiphase alternating-voltage supply means having a plurality ofmutually phase-displaced output voltages of respectively differentamplitudes, controllable rectifiers connecting said respective outputvoltages to said load circuit for applying rectified auxiliary voltagesupon said load circuit when said rectifiers are conductive,condition-responsive control means connected to said rectifiers forcontrolling them to conduct only during a given interval of time,circuit means for effecting removal of said auxiliary voltages, saidcontrol means being in connection with said load circuit and responsiveto respective first and second changes occurring in said load circuitdue to opening of said control switch means so as to apply saidauxiliary voltages during decay of the field of said device, saidauxiliary voltages forming a resultant fluctuating voltage opposed tothe induction voltage of said device for shortening said decay
 6. Asystem according to claim 5, comprising a multiphase power supplytransformer, said direct-current supply means comprising controlledrectifier means connected to said transformer for providing said normaloperating voltage, said transformer forming part of saidalternating-voltage supply means, and said resultant fluctuating voltagehaving a higher absolute value than said operating voltage.
 7. In asystem according to claim 6, said condition-responsive control meansbeing responsive to the forward current which in said load circuitcontinues to flow through said controlled rectifier means upon openingof said control switch means, whereby said forward current constitutessaid first change which causes said resultant auxiliary voltage to beapplied.
 8. A system for rapid field excitation control of anelectromagnetic device, comprising direct-current supply means having aload circuit including said device for providing normal operatingvoltage therefor and having control switch means for switching saidoperating voltage on and off; multiphase alternating-voltage supplymeans having a plurality of mutually phase-displaced output voltages ofrespectively different amplitudes, controllable rectifiers connectingsaid respective output voltages to said load circuit for applyingrectified auxiliary voltages upon said load circuit when said rectifiersare conductive, condition-responsive control means connected to saidrectifiers for controlling them to conduct only during a given intervalof time, said control means being in connection with said load circuitand responsive to respective first and second changes occurring in saidload circuit due to opening of said control switch means so as to applysaid auxiliary voltages during decay of the field of said device, saidauxiliary voltages forming a resultant fluctuating voltage opposed tothe induction voltage of said device for shortening said decay, amultiphase power supply transformer, said direct-current supply meanscomprising controlled rectifier means connected to said transformer forproviding said normal operating voltage, said transformer forming partof said alternating-voltage supply means, and said resultant fluctuatingvoltage having a higher absolute value than said operating voltage, saidcondition-responsive control means being responsive to the forwardcurrent which in said load circuit continues to flow through saidcontrolled rectifier means upon opening of said control switch means,whereby said forward current constitutes said first change which causessaid resultant auxiliary voltage to be applied, saidcondition-responsive control means being responsive to at least one ofsaid rectifier means in said load ciRcuit changing to the off-state,whereby said change of state constitutes said first change which causessaid resultant auxiliary voltage to be applied; and saidcondition-responsive control means being further responsive to anotherone of said rectifier means changing to the off-state, whereby saidlatter change causes said resultant auxiliary voltage to be switchedoff.
 9. A system according to claim 5, comprising a synchronizing stageconnected with said control switch means and with saidcondition-responsive control means for securing a given switching-onpoint of said fluctuating auxiliary voltage relative to its cycleperiod.
 10. A system according to claim 5, comprising a multiphasetransformer having a plurality of secondary windings, first and secondcontrollable rectifier means having respective control electrodes, saidfirst controllable rectifier means being connected to respective ones ofsaid secondary windings and to said device for supplying an operatingfield voltage to said device, said second controllable rectifier meansbeing connected to other ones of said secondary windings and to saiddevice for supplying an increased auxiliary field voltage to saiddevice, firing control circuit means comprising three firing circuits, afirst one of said firing circuits being connected to said controlelectrodes of said first rectifier means, a second and the third one ofsaid firing circuits being coupled to said first firing control circuitand connected to said control electrodes of said second rectifier means,sensing circuit means coupled to said second and third firing circuitsand thereby to said first firing circuit for discontinuing the firing ofany one of said first and second rectifier means in response to sensingof a change in the excitation of said device, control switch meansarranged in said first firing circuit for closing said first firingcircuit to cause initial energization of all of said rectifier means,said sensing circuit means being adapted, when responding, to causeblocking of said second rectifier means after a predetermined periodfollowing the closing of said switch means, said switch means being alsooperative to cause blocking of said first rectifier means when saidswitch means is opened.
 11. A system according to claim 10, comprising afurther rectifier circuit for energizing said firing control circuitmeans, said firing control circuit means comprising flip-flop meansconnected between said further rectifier circuit and the controlelectrodes of said second rectifier means, and synchronizing means insaid firing control circuit means for setting the firing of said secondrectifier means at a predetermined point relative to the wave of theincreased voltage.
 12. In a system according to claim 11, said flip-flopmeans comprising two monostable flip-flop stages of which each hascomponents complementary to those of the other flip-flop stage, saidflip-flop stages having control electrodes and supply electrodes andoutput electrodes, the control and supply electrodes of at least one ofsaid flip-flop stages being couple through said control switch means tosaid further rectifier circuit, said synchronizing means comprising anRC member for connecting the synchronizing means to one of saidsecondary windings of said transformer.
 13. In the system according toclaim 12, said one monostable flip-flop stage comprising an adjustablemember connected to said control electrode for adapting the circuitarrangement to respectively different electromagnetic devices.